I have two Radeon 6450 graphics cards in my computer, with three screens. Only the screens plugged into the first graphics card are recognized and configurable in the displays setting panel. How can I use the displays plugged into my second graphics card?

Can you post a screenshot of what you see in System Settings>Displays? The 6450 has three outputs AFAIK...VGA, DVI and HDMI, can't you connect your three monitors on one card? If your monitor doesn't have an HDMI port, can you try with a TV that does?
–
titaniumtuxApr 10 '12 at 20:17

i've added an image of the displays panel. the HDMI port does indeed give me a third screen, but i would still like to find a way to use the second card as i would like to purchase another 27" screen and would need to use the second card for that.
–
notatoadApr 10 '12 at 20:55

1

@ChristianVielma It's definitely possible. Look at USB-VGA adapters. Some of them work, some of them don't but saying using two cards is not possible is surely incorrect.
–
hbdgafApr 12 '12 at 21:42